Typical automotive passenger airbag systems consist of a gas generator, cushion and housing. Most systems use a cylindrical pyrotechnic type gas generator. As described in Davis et al., U.S. Pat. No. 4,380,346 issued Apr. 19, 1983, one of the characteristics of a pyrotechnic gas generator is that as the environmental temperature increases, the rate of gas generation also increases. This change in burn rate causes a corresponding change in cushion deployment performance. During a hot temperature deployment, the cushion fills faster and more aggressively than during a cold or ambient (normal) temperature deployment. Since most crash induced deployments occur around the normal range, this creates a need for a low cost method to reduce the stress levels on the cushion and housing when a hot temperature employment occurs. To compensate for this, Davis et al. provide perforations in the inflator housing and foil covers for the holes designed to rupture at desired pressures. Because the inflator is housed in the module housing, the pressure relief is only temporary and the pressure continues to build up in the module housing and in the airbag cushion.
In another recent patent, Zander et al. U.S. Pat. No. 4,902,036, issued Feb. 20, 1995, a weld provided in the inflator housing ruptures when the generator over-pressures, thereby relieving the pressure buildup in the inflator.
In still another recent U.S. patent, Burnard et al. U.S. Pat. No. 5,346,251 a groove is provided in an inflator housing for the same purpose.
Neither of these two latter provisions is entirely satisfactory because when the inflator housing ruptures, fragments of metal can be ejected into the interior of the vehicle thereby endangering the occupant of the vehicle. Furthermore, both Zander and Burnard describe driver side airbag devices in which the rupturable structure is not enclosed in a module housing.
The present invention provides a simpler low cost means for regulating pressure in a passenger side airbag inflation module when automotive airbags are deployed. In the present invention, a valve in the module housing opens when the pressure inside the module reaches a selected value, and there is no danger of metal fragments being ejected into the vehicle.